As a heat-insulating container made paper mainly used for instant dried Chinese noodles, there has widely been used a container in which a paper cup body surrounded over its outer periphery with a heat-insulating corrugated member subjected to a process so as to make an alternate arrangement of narrow projections and recesses in the longitudinal direction of the cup body.
In Japanese Patent Provisional Publication No. H8-113274, there is proposed a heat-insulating container in which a change in its cross-sectional shape is made so that the total area of concave portions on the outer surfaces of the container is decreased and the total area of flat portions thereon is increased. Such a container has been put to practical use.
In Japanese Patent Provisional Publication No. H4-45216 and Japanese Patent Provisional Publication No. H8-104372, there is proposed a heat-insulating container, in which a heat-insulating member subjected to a corrugating process or an embossing process so that no irregularity is formed on the outer surface of the container.
In Japanese Utility Model Provisional Publication No. 4-45212, there is made, on the other hand, a proposal that a heat-insulating property is given by a gap formed between a double-walled cup body.
The above-described container having the cup body surrounded with the heat-insulating corrugated member has a problem that the container has an unnecessarily larger thickness even in the upper portion thereof, which is not brought into contact with a hand, regardless of the cross-sectional shape of the heat-insulating member. The irregularity on the outer surface of the container may become obstacle to a high grade design to be given to the container, and characters, patterns and the like printed on the surface thereof may be made unclear and vague, thus causing problems.
In order to solve such problems of the external appearance of the container, there is made a proposal to cause the above-mentioned container to be surrounded with an additional liner or thin sheet of paper in Japanese Utility Model Provisional Publication No. S49-87479 and Japanese Utility Model Publication No. H4-45216. The container obtained in accordance with such a proposal has an uneconomic problem that the high production cost is required, an external appearance problem that the heat-insulating container may has the irregular bottom and the narrow projections and recesses or the embossed portions may be visible from the bottom, and an unhygienic problem that dust or a liquid may enter gaps of these portions.
FIG. 43 is a cross-sectional view of a conventional heat-insulating container 50 proposed in Japanese Utility Model Provisional Publication No. H4-45212. The heat-insulating container 50 is obtained by inserting a paper cup body 51 composed of a bottom plate 52 and a side wall 3b3 having an outward curled top portion 54 into a sleeve 55 provided on its lower end with an inward curled portion 56, and integrally combining the cup body 51 and the sleeve 55 with each other at the upper and lower contact portions of them. A heat-insulating space is formed with the utilization of the thickness of the curled portion 56 of the sleeve 55.
Such a heat-insulating container 50 does not use any specific heat-insulating member and has therefore no disadvantage caused by the heat-insulating member. When the container is actually held at the central portion of the side wall thereof with a hand, the sleeve 55 may however easily be warped inward to decrease the capacity of the heat-insulating space, thus deteriorating the heat-insulating property.
In addition, a container in which a sleeve is disposed on an outer periphery of a cup body is also proposed, for example, in Japanese Utility Model Provisional Publication No. S52-97282, and Japanese Patent Provisional Publication No. H4-201840. The container disclosed in these publications is provided with an outward projecting rib and the sleeve bonded to the rib.
However, in such structure, since the rib is formed into a round or triangular shape in its cross-section, only a ridge portion of the rib contacts the sleeve, so that a bonding area between the rib and the sleeve reduces, causing the lack of the bonding strength. Since the position of the rib changes variously in accordance with the type of the container, it is necessary to adjust the position to which the adhesive agent is applied in accordance with the position of the rib, so that a preparation for the process may be troublesome. In particular, if the rib functions as the Peter line indicating proper level of liquid poured in the container, the position of the rib often changes in accordance with a kind of a product packaged in the container, and thus the above mentioned problem may be more serious. Also, if the Peter line is adjacent to the curled portion of the cup body, distance between the sleeve and the cup body reduces and the resistance force during the combination process may increase to thereby cause an assembling error.
Further, it is desired to provide an apparatus capable of producing the container efficiently. In particular, it is preferable to form the sleeve completely without changing a mandrel on which a sheet-like blank as a material of the sleeve is curled. It is also desired to assemble the sleeve and the cup body correctly and efficiently.
Furthermore, it is particularly desired to provide an apparatus capable of facilitate a process for forming the rib on the side wall of the cup body. In Japanese Patent Provisional Publication No. H4-97833, there is disclosed a rib-processing apparatus in which an expandable chuck is inserted into the cup body, and the chuck expands outward at a predetermined position in the cup body to enlarge the container outside, thereby forming the rib.
However, since the apparatus disclosed in the above publication forms the rib on the side wall of the cup body all at once over an entire periphery thereof, it is necessary to add a relatively great force to the side wall with using force-magnification means, such as a wedge or the like, even if the rib is relatively small. Therefore, it is difficult to form a large rib. Also, since the chuck is driven in the cup body, it is necessary to locate one part of a driving mechanism for the chuck in a narrow space in the cup body, so that structure of the mechanism becomes complex. It needs a long time to take the chuck in and out against the cup body, so that it is difficult to form the rib efficiently.